The present disclosure is directed to an endovascular aneurysm occlusion device and methods for occluding aneurysms. More particularly, the present disclosure is directed to an endovascular aneurysm occlusion device that includes a biocompatible polymeric member and a biocompatible metallic frame member. In one exemplary method for occluding a cerebral aneurysm, the biocompatible polymeric member is introduced into the aneurysm and then the biocompatible metallic frame member is introduced into the polymeric member to expand the device to the shape of the aneurysm. Device placement leads to biological isolation of the aneurysm and initiates a cascade of wound healing events at the aneurysm site that provides for improved patient outcomes.
Cerebral aneurysms may form due to damage to the internal elastic lamina of blood vessels by hemodynamic factors. Weakening of the vessel wall leads to formation of a bulge known as an aneurysm. As many as 5 million individuals in North America may harbor cerebral aneurysms. (Broderick J P et al., J Neurosurg 78, 188 (February 1993)). Cerebral aneurysms are at risk of rupture, which is referred to as subarachnoid hemorrhage (SAH). SAH is a devastating condition with high morbidity and mortality. In the U.S., SAH is associated with an annual cost of $1.75 billion. To avoid further complications, un-ruptured and ruptured aneurysms need to be treated. Immediate and long-term obliteration of the aneurysm is important to prevent subsequent growth and rupture.
The majority of cerebral aneurysms are currently treated from inside of the blood vessel, which is referred to as the endovascular route. Endovascular devices used to occlude aneurysms include coils (very common), intravascular injections, and detachable intravascular balloons. During coil embolization (or, “coiling”), metal components made from platinum (Pt) or nickel titanium (NiTi) are threaded through a catheter and deployed into the aneurysm. A primary goal of the operation is to densely fill the aneurysm cavity with coil loops, which block blood flow into the aneurysm and prevent rupture. The aneurysm is blocked by interlaced coils, which gradually form a collagen membrane isolating the aneurysm from circulation. Use of these coils is accompanied by numerous complications, however.
One significant drawback with known coiling occlusion devices is coil compaction over time which leads to incomplete aneurysm occlusion in approximately 30% of cases. (Cognard C et al., Radiology 212, 348 (August 1999). Such incomplete occlusion causes aneurysm enlargement and subsequent rupture. Another significant drawback associated with known occlusion coils is blood clotting in the aneurysm. Yet another drawback associated with known occlusion coil treatments is unpredictability of aneurysm healing. Still another drawback of known aneurysm treatments is imprecise placement of numerous coils into the aneurysm, one by one, until the entire aneurysm is filled. Larger sized aneurysms require time-consuming placement of many coils, which leads to increased risk of morbidity and mortality while the patient is under general anesthesia. Placement of each individual coil into the aneurysm is also a procedural risk, which increases morbidity and mortality of the procedure.
Another approach that has been utilized to treat cerebral aneurysms includes filling the aneurysm with a liquid embolic agent and allowing the liquid embolic agent to harden over time (generally through crosslinking when contacted with blood) and occlude the aneurysm. This method, however, has numerous shortcomings including the lack of any containment mechanism for the liquid embolic agent once injected into the aneurysm. It has been found that lack of containment of the liquid embolic agent can result in leakage into normal circulation prior to solidification. This leakage can ultimately lead to blood vessel occlusion and stroke. Further, the lack of containment can also result in incomplete filling of the aneurysm and a decrease in effectiveness of the treatment. Additionally, when this approach has been utilized there have been reports of problems filling the vascular defects with the embolic liquid as the leading surface of the embolic liquid being injected into the aneurysm reacts and hardens thus making complete injection into the aneurysm very difficult.
Polyurethane copolymers have been widely used for numerous biomedical applications due to their excellent mechanical properties, biocompatibility, and hemocompatibility. In contrast to other materials used in vascular applications, such as polytetrafluoroethylene (PTFE) and polyethylene terephthalate (PET), polyurethane-based materials support the growth of endothelial cells and possess mechanical properties that match the native vasculature. (Tiwari A et al., Cardiovascular surgery (London, England) 10, 191 (2002).
Surface and/or bulk modification of polyurethane may be accomplished, such as by attaching biologically active species to reactive groups on the polyurethane molecule. Such modifications may be designed to control/mediate host wound healing responses. However, polyurethane is not inherently bioactive.
Hyaluronic acid (HA) and heparin are glycosaminoglycans (GAGs) found in all mammals. Hyaluronic acid is a unique and highly versatile biopolymer. Hyaluronic acid plays a vital role in embryonic development, extracellular matrix homeostasis, wound healing, and tissue regeneration. However, the exact mechanisms of hyaluronic acid's regulation of these events are unknown. The behavior and cell influences of hyaluronic acid are highly dependent upon its concentration and molecular weight. Biomaterials made from derivatized and cross-linked hyaluronic acid have been reported in the bioengineering community for applications such as orthopedic, cardiovascular, opthalmology, dermatology, and general applications in tissue engineering, surgery and drug delivery. Hyaluronic acid is naturally derived and nonimmunogenic. It also has multiple sites for modification and inherent biological activities. (Leach J B et al., Encyclopedia of Biomaterials and Biomedical Engineering 2004, p. 779).